CAD/CAM implant surgical guides: maximum errors in implant positioning attributable to the properties of the metal sleeve/osteotomy drill combination.

BACKGROUND: The purpose of this study is to provide the relevant equations and the reference tables needed for calculating the maximum errors in implant positioning attributed to the properties of the mechanical parts of any CAD/CAM implant surgical guide, especially the in-office manufactured ones.

METHODS: An algorithm was developed and implemented in C programming language in order to accurately calculate the maximum error at the apex, error at the neck, vertical error at the apex and deviation of implant axis, between the planned and the actual implant position. The calculations were based on the parameters of total length (= implant length + offset), offset (distance from neck of implant to the lip of the metal sleeve), clearance (space between the bur and the sleeve), sleeve length. The variability of the parameters was constrained: (1) implant length, 8-18 mm; (2) sleeve length, 4-7 mm; (3) clearance, 50-410 μm; and (4) offset values, 6-17 mm. Multiple regression analysis was conducted to quantify the relationship between the error at the apex and the error at the neck and various predictors.

RESULTS: The equations used for the bespoke estimation of the errors in implant positioning along with three reference tables of the various errors tabulated are presented. The maximum error at the apex of the implant was computed 2.8 mm, the maximum deviation of the implant axis 5.9° and the maximum error at the neck (entrance) of the implant was estimated 1.5 mm. The vertical error between the planned and actual implant position can be considered negligible (< 0.1 mm).

CONCLUSIONS: The results of this study compute part of the expected differences in final clinical implant position when any CAD/CAM surgical guide is used. Given that the implantologist, with the capability of an in-office digital designed and 3d printed surgical guide, can readily decide upon the dimensions of the metal sleeve, the clearance between the osteotomy bur and the sleeve, and the design of the guide in relation to the distance of the lip of the sleeve to the implant neck (offset), in order to minimise the inevitable errors.